The thing, though, is... you take a virus, put it in a petri dish by itself, and it does... nothing.

It doesn't have a metabolism, it doesn't look for a host, it doesn't do anything... it's just an inert clump of organic matter. (Then again, probably the same could be said for, say, spores. Or pollen. Or raw DNA or even RNA. Are those alive..?)

But plug it into a cell and... well, it sort of breaks apart, injecting it's RNA or DNA into the cell, and... that's it for that particular instance of the virus.

Sure, the cell will then take that genetic payload and unwittingly use it to fabricate as many copies of the virus as it can... but at that point the original virus instance is just an empty protein husk... is it still alive..? Does “being alive” maybe not apply to individual virus particles, but to this whole process..?

Maybe being alive is not just a binary, but a scale (or something more complex) where you can fit anything from crystals or prions to us and who knows what else, maybe whole ecosystems, maybe the Gaia concept of a living world...

But we humans certainly do seem to like our black and white binary choices, even if viruses might be a triangular peg we're trying to fit into either a round or square hole...